For lack of a better term. If you look at the edge of the branch and the squirrel, theres like a haze or halo along their edges. This is a 100% crop of this section. Sun was behind me, but mostly blocked by this tree area.

Is this something caused by the camera or lens, or just a digital image at 100%?

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That's 'purple fringing', a.k.a. chromatic aberration, or 'c.a.'. An optical shortcoming of the lens system that becomes apparent at certain angles to, and levels of the available light.
Foliage against a bright sky is notorious for bringing it out.
Better lenses have less of it, obviously. But the trade-off is, just as obviously: price.

I believe the D90 will also correct for CA, but only with Nikon lenses. The CA is caused by the different channels of light passing thru the elements and not aligning at exactly the same spot on the sensor. Nikon apparently compensates for the "misalignment" with Nikon lenses, but you probably don't get the same feature with non-Nikon lenses.

You can correct most of it in Adobe Camera Raw and in Photoshop CS/Elements.